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Biomedical subjects

J van Aken

Publications and source records attributed to J van Aken.

At least 37 records · Page 2Linked to original sources
PubMed1990

Effective dose equivalent to the operator in intra-oral dental radiography.

The effective dose equivalent to the operator in intra-oral dental radiography has been determined. The exposure from a bitewing radiograph and periapical views of the left maxillary incisors and first molar was measured at nine heights and 16 positions, all 1 m from the patient. The effective dose equivalent was determined using data from ICRP 51 (International Commission on Radiological Protection: Data for Use in Protection Against External Radiation). The values presented are related to an exposure of 1 C kg-1 (3876 R) measured free in air at the tube-end. They thus constitute ratios which are not influenced by the sensitivity of the film or other detector used and form standard tables which permit the calculation of the effective dose equivalent in clinical situations.

Dental Staff↗
PubMed1989

The detection of in vitro produced periodontal bone lesions by conventional radiography and photographic subtraction radiography using observers and quantitative digital subtraction radiography.

Changes in the periodontium produced by removal of bone cylinders at one interdental site of a dry human mandible, were recorded radiographically. These artificial lesions had diameters of 0.3 mm increasing to 1.4 mm in steps of 0.1 mm. Radiographs were obtained using 3 different X-ray tube potentials and 3 different amounts of radiation. These 9 exposure variables resulted in 9 series of radiographs from the artificial lesions. Observers were asked to determine the presence or absence of these periodontal bone lesions on conventional radiographs and on photographically subtracted images. The images were also evaluated by a quantitative digital subtraction technique. This study showed that the smallest periodontal bone changes were detected with the quantitative digital subtraction technique compared to the other methods using observers. On photographically subtracted images, smaller bone changes were detected by the observers than on conventional radiographs. Only the detection threshold of the quantitative digital subtraction technique was influenced by the 2 exposure factors: kVp and mAs.

Alveolar Process↗
PubMed1989

The effect of in-vivo-occurring errors in the reproducibility of radiographs on the use of the subtraction technique.

A device for serial radiography in maxillary and mandibular premolar and molar regions was developed. Radiographs of 9 patients were made during a period of 1 year. When testing the device, the influence of the time interval between the radiographs and the influence of the construction of the device on the reproducibility of the X-ray images were determined. An increase of the time interval between radiographs reduced the reproducibility. The use of bilateral bite blocks improved the reproducibility of the X-ray images in comparison with the images obtained with a device with a one-sided bite block. Errors in the reproducibility caused differences in the image geometry of radiographs. The in-vivo-found differences were studied for their effect on the detection threshold of observers using photographic subtraction radiography. An increase of the differences in image geometry between the radiographs resulted in a higher detection threshold and a higher % of false positive decisions. It appeared that very small differences between clinical radiographs, corresponding with an angulation error of 0.7 degrees, can be tolerated in order to prevent the occurrence of high numbers of type-I errors. The % of radiographs, which met this requirement and could be used for photographic subtraction radiography, was 55%, when taken at time intervals of 1 year.

Adult↗
PubMed1989

Problems around the in vitro and in vivo application of quantitative digital subtraction radiography.

The validity of a quantitative digital subtraction technique was investigated in vitro when influenced by the following aspects: the material enveloping the aluminium reference wedge, the radiation quality used to produce the radiographs and the effect of differences in image geometry between repeated radiographs. The test object consisted of a dry mandible in which small test objects made of aluminium with known volumes were introduced. By means of the quantitative digital subtraction technique, the aluminium volumes of these test objects were determined. The best agreement between the measured volumes and the actual volumes, was found when the aluminium reference wedge was embedded in polymethylmethacrylate and exposure conditions of 50 kVp, 15 mAs were used. An increase in the differences in image geometry between radiographs led to a decrease in the validity and accuracy of the measurements. For the in vivo application of this method, serial radiographs of 4 patients were taken to register the periodontal bone changes over a 5-8 month period. Differences in the approximal bone between radiographs were quantified in aluminium equivalent volumes (AEV's). In 23% of the measured sites, changes in the mineral content could be detected. The changed sites were found in only 2 patients. One patient showed 3 sites with remineralization, while the other patient showed 2 sites with demineralization. The differences detected ranged from -1.54 to +0.38 mm3 aluminium equivalent.

Aluminum↗
PubMed1989

[Quality of dental radiographs. A sample from 52 general practices].

To assess the quality of dental radiographs in general practice, 1000 radiographs in 52 practices were collected and evaluated. The radiographs were judged by two examiners using standard series of X-ray film, showing different degrees of the nine different types of errors studied. Furthermore, the diagnostic quality was assessed; if the diagnostic value was poor, the cause was registered. Only 3.1% of the investigated radiographs met all the criteria, and the quality of 13.4% was found to be poor. The main causes were filmpositioning, density and errors in the category 'residual'. It also appeared that a combination of errors in one radiograph, which were individually not very serious, resulted in an unacceptable radiograph.

Humans↗
PubMed1982

The optimum circular field size for dental radiography with intraoral films.

Intraoral radiographs are often made with circular fields to irradiate the film, and in many instances these fields are much larger than the film. The feasibility of reducing a circular radiation field without increasing the probability of excessive cone cutting was evaluated clinically, and an optimum field size was determined. A circular radiation field 4.5 cm. at the tube end was found to minimize cone cutting and reduce the area of tissue irradiated by at least 44 percent. Findings suggest that current I.C.R.P. recommendations for a 6 to 7.5 cm. diameter circular field may be too liberal.

Humans↗
PubMed1979

The length of teeth. A statistical analysis of the differences in length of human teeth for radiologic purposes.

Intraoral radiograms can be made according to the long tube paralleling technique utilizing aiming devices. An important factor in the design of these instruments is the length of the teeth to be radiographed. Reliable data regarding the length of the teeth in the different regions of the mouth are not available. Information on the length of teeth was therefore collected by measuring 1,400 extracted teeth. A statistical analysis of the data finally resulted for each region of the mouth and for both sexes in length value which could be used for the design of aiming devices.

Bicuspid↗
PubMed1979

Factors influencing the design of aiming devices for intraoral radiography and their practical application.

Intraoral roentgenograms can be made according to the long-tube paralleling technique utilizing aiming devices. These instruments consist of a bite block, an indicator rod, and a collimator plate. For the position of the film in relation to the bite block surface, the following data are decisive and therefore studied: the length of the teeth to be radiographed, the enlargement as a result of the divergence of the x-ray beam, and the periapical area necessary for the interpretation and mounting of the roentgenograms. As a result, the bite blocks of the instruments were provided with three vertical steps to permit different film positions needed for the specific situation in the different regions of the mouth. The use of the correct film positions results in roentgenograms with a high diagnostic value. In order to reduce the patients radiation dose the aiming devices include a collimator plate. A description is given of the data used for the design of the plate.

Dental Instruments↗
PubMed1979

Influence of enflurane on cerebral blood flow in man.

Cerebral blood flow was measured by means of a 10-channel cerebrograph in anesthetised patients before and during 2% enflurane. This investigation was carried out after carotid angiography; 2-3 mCi Xe133 was injected into the internal carotid artery. The clearance curves of Xe133 were captured by 10 scintillation counters. In addition to regional cerebral blood flow (rCBF), arterial blood pressure, heart rate, stroke volume, cardiac output and arterial blood gases were measured in seven adult patients. During 2% enflurane, a small, and in two regions a significant decrease in rCBF was observed. Mean arterial pressure and heart rate decreased significantly, but cardiac output did not. The decrease in PaCO2 was not significant.

Anesthesia, Inhalation↗
PubMed1979

Tomography of the lamina dura.

Tomographic technics are based on the principle that when the X-ray source is moved in relation to the object the speed of the projection of different parts of the object on a plane will be different. By selecting the projections which have a certain speed, an image of a selected plane of the object can be obtained. Two principles have to be considered: 1. the image of a curved surface will only show the surface area where the rays form a tangent to the surface; 2. in tomography the blurring of the image increases with an increase of the tomographic angle and the distance of the object to the plane in focus. The image formation of curved bony surfaces, such as the lamina dura, is discussed in detail. The specific properties of the spatial model of the lamina dura requires another approach to explain the image formation. Diagrams and graphs illustrate the effect of the tomographic movement of the X-ray source on the movement of the projected image. Limits for the misalignment permitting an interpretable image are given, as well as an explanation of the images obtained when these limits are exceeded.

Alveolar Process↗
PubMed1976

Paget's bone disease treated with diphosphonate and calcitonin.

Patients with biochemically active Paget's disease were treated with a combination of disodium ethane-1-hydroxy-1, 1-diphosphonate (E.H.D.P.) and synthetic human calcitonin in low doses. The effect on biochemistry was greater and more consistent than that of even higher doses of human calcitonin. Bone biopsy showed decrease or even disappearance of abnormal osteoblasts and osteoclasts from pagetic lesions, and the addition of calcitonin to E.H.D.P. prevented the development of mineralisation defects.

Aged↗